DESCRIPTION: The proposed research investigates the development of phonological categories by children with functional phonological disorders. The primary focus is on default categories of language, which are presumed to be the universal properties most basic to a sound system, and the building blocks from which all other phonological categories emerge. The fundamental hypothesis to be tested is that, when a child initiates the acquisition process with a default other than the universal, this will have repercussions for subsequent elaboration and restructuring of the sound system, so much so that it may actually impede learning and put the child at-risk for change. Two projects involving 60 children, aged 3;0 to 7;6, are planned to examine defaults at different levels of language structure associated with place of articulation in fricatives and with consonant clusters. In both projects, converging evidence will be brought to bear on the status of defaults in acquisition, and will include phonological descriptions, conceptual testing, learning patterns, and computational analyses. Theoretically, the results will address the universal versus child-specific nature of defaults, the convergence of defaults in representation and processing, and the similarity of defaults across hierarchical levels of linguistic structure. Clinically, the consequences of defaults for learning will be determined, and the efficacy of treatment in inducing change in defaults will be established.